Describe your speech patterns in different social situations

Recently, I was talking to a salesperson at a car dealership near my home, in California. At first I assumed that he was from California, because he didn’t have any particular phonological features that would mark him as being from some other part of the country. But while talking with me, he used the expression you might could…(meaning ‘It’s possible that you could…’), a feature we don’t use in California. I asked where he was from. He said that his father had worked for the government, and that growing up he had moved around a lot (which accounted for his lack of a clear regional accent). But he had also spent a large chunk of his childhood in Alabama, a place that does have might could. In fact, when I asked where he was from, he said, “Alabama,” before giving me the rest of the explanation about moving around. And he’d carried might could with him in his linguistic suitcase, all the way to California. Clearly, even small features of our speech can indicate things about our backgrounds.

misty passage from the question